1. Field of the Invention
The present invention relates to a flame-retardant polycarbonate resin composition and its injection moldings. More precisely, it relates to a flame-retardant polycarbonate resin composition in which the flame retardant exhibits good flame retardancy without bleeding out of the moldings of the composition, and also to its injection moldings having the advantages of good outward appearance and good mold releasability. In particular, when combined with a styrenic resin, the composition of the invention still has good melt fluidity and good moldability and is readily formed into moldings having good impact resistance.
2. Description of the Related Art
As having the advantages of impact resistance, heat resistance and good electric properties, polycarbonate resins have many applications in various fields of, for example, office automation appliances, information appliances, electric and electronic appliances for industrial and household use, car parts and machine materials. As a rule, polycarbonate resins are self-extinguishable. However, some of their applications to office automation appliances, electric and electronic appliances for industrial and household use and others require high-level retardancy. To meet the requirement, various flame retardants are added to polycarbonate resins. One conventional method for making polycarbonate resins have flame retardancy comprises adding thereto a halogen-containing flame retardant such as a bromine compound or the like having high flame retardation capabilities alone with a flame retardation promoter such as antimony oxide or the like.
However, in view of the recent problems with the environment and of the safety, it is desired not to use halogen compounds such as bromine compounds, chlorine compounds and the like for making resins have flame retardancy. Regarding non-halogen flame retardants, various methods have been proposed of using phosphate compounds. On the other hand, there are some problems with polycarbonate resins in that they require high molding and working temperatures and their melt fluidity is low. As requiring relatively high molding and working temperatures, polycarbonate resins, especially those containing various additives are often problematic in that their thermal stability is poor while they are molded and worked and that their moldings could not exhibit their good properties. Where polycarbonate resins are molded into parts or housings of office automation appliances such as duplicators or facsimiles or those of electric and electronic appliances, the moldings shall have a complicated shape with local projections or depressions, for example having ribs or bosses therewith, and are required to be lightweight and thin-walled from the viewpoint of resources saving. Therefore, desired are polycarbonate resin compositions having increased melt fluidity, or that is, having increased injection moldability. Various polycarbonate resin compositions having increased moldability have heretofore been proposed, to which are added rubber-like polymer-modified styrenic resins in consideration of the physical properties such as impact resistance of the moldings of the compositions.
Compositions of polycarbonate resins to which are added styrenic resins such as acrylonitrile-butadiene-styrene resins (ABS resins), acrylonitrile-styrene resins (AS resins) and the like for the purpose of improving the melt fluidity of the resin compositions are known as polymer alloys, and have many applications in the field of moldings as having good heat resistance and impact resistance. Of their applications, where such polycarbonate resin compositions are used for office automation appliances, electric and electronic appliances and the like, they are required to have high flame retardancy of not lower than a predetermined level so as to ensure and increase the safety of their moldings.
To meet the requirements as above, various methods have heretofore been proposed. Concretely, JP-A 61-55145 discloses a thermoplastic resin composition comprising (A) an aromatic polycarbonate resin, (B) an ABS resin, (C) an AS resin, (D) a halogen compound, (E) a phosphate, and (E) a polytetrafluoroethylene component. JP-A 2-32154 discloses a molding polycarbonate composition with high flame retardancy and high impact resistance, comprising (A) an aromatic polycarbonate resin, (B) an ABS resin, (C) an AS resin, (D) a phosphate, and (F) a polytetrafluoroethylene component. JP-A 8-239565 discloses a polycarbonate resin composition comprising (A) an aromatic polycarbonate, (B) an impact-resistant polystyrene resin with rubber-like elastomer, (C) a non-halogen phosphate, (D) a core/shell-type, grafted rubber-like elastomer, and (E) talc.
These are all to improve the melt fluidity and therefore the moldability of polycarbonates, and to improve the impact resistance and the flame retardancy of the moldings of polycarbonates. As having such improved properties, the polycarbonate compositions proposed are formed into various practicable moldings. However, in the field of office automation appliances, electric and electronic appliances for household or industrial use, parts and housings of those appliances are required to be more lightweight and thin-walled. In particular, their shape is being more complicated to have fine projections and depressions such as ribs and bosses therewith or have a lattice structure, so that they are applicable to any complicated and large-sized appliances. In that situation, polycarbonate resins are required to have better moldability enough to meet the requirements as above.
As a rule, phosphate compounds that are liquid at room temperature and have a low melting point are used as a flame retardant for polycarbonate resins, but their amount to be added to the resins for attaining the intended flame retardancy of the resins is relatively large. Therefore, such phosphate compounds are often problematic and defective in that the resin moldings comprising them are deposited and that they lower the heat resistance and the impact resistance of the resin moldings. To solve the problems with those phosphate compounds that bleed out of the resin moldings and lower the heat resistance of the resin moldings, some methods have been proposed. For example, JP-A 6-228426 discloses a method of adding both (B) an alkyl-substituted aromatic phosphate compound having a specific structure and having a high viscosity and (C) a triphenyl phosphate or the like to (A) a polyphenylene-ether resin or a polycarbonate resin. JP-A 7-179715 discloses a flame-retardant resin composition comprising from 1 to 99 parts by weight of (A) a polycarbonate resin, from 1 to 99 parts by weight of (B) a rubber-reinforced resin, and from 0.1 to 30 parts by weight, relative to 100 parts by weight of the total of (A) and (B), of (C) an organic phosphorus compound having a melting point of not lower than 120.degree. C. JP-A 8-12867 discloses a thermoplastic resin composition comprising 100 parts by weight of a resin mixture of 50 to 98% by weight of (A) an aromatic polycarbonate and from 2 to 50% weight of (B) an ABS resin and/or (C) an AS resin, from 0.01 to 5 parts by weight of (E) a fluorine resin and/or a silicone, and from 1 to 40 parts by weight of (E) a phosphate compound having a high melting point. In these, phosphate compounds having a high viscosity or a high melting point are used as the flame retardant to solve the problems, and they are effective in some ways.
Through our studies, however, we, the present inventors have found that, though the phosphate compounds having a high melting point could solve the problem of bleeding, they have another problem of poor dispersibility thereby having some negative influences not only on the outward appearance of resin moldings comprising them but also on the flame retardancy thereof. Especially when the phosphate compounds of that type are in compositions comprising a polycarbonate resin and a styrenic resin, we have further found that the ability of the styrenic resin to improve the melt fluidity of the compositions is poor, that the impact resistance of the moldings of the compositions is not satisfactory, and that the mold releasability of the moldings is poor and therefore must be improved.